Vehicle speeds in South Australia CN Kloeden, JE Woolley

Transcription

1 Vehicle speeds in South Australia 7 CN Kloeden, JE Woolley CASR REPORT SERIES CASR April 9

2 Report documentation REPORT NO. DATE PAGES ISBN ISSN CASR April TITLE Vehicle speeds in South Australia 7 AUTHORS CN Kloeden, JE Woolley PERFORMING ORGANISATION Centre for Automotive Safety Research The University of Adelaide South Australia AUSTRALIA SPONSORED BY Department for Transport, Energy and Infrastructure Post Office Box Walkerville SA 8 AUSTRALIA AVAILABLE FROM Centre for Automotive Safety Research ABSTRACT A program designed to monitor the speed behaviour of motorists commenced at sites in South Australia in 7. The sites selected included sites with historical measurements supplemented by new sites to give a broad range of road types. Speed data was collected for one week at each of the sites and summary volume and speed statistics and speed distributions are given for each of the road types surveyed. Limited historical surveys on a set of roads in built up areas indicated that travelling speeds on those roads fell in (after the introduction of the default km/h speed limit in March ) compared to and fell again in. However, travelling speeds on those roads increased in 7 compared to by a statistically significant amount at least on Adelaide local roads affected by the km/h limit. Analysis of previously collected data for a limited subset of rural roads indicated no statistically significant change in vehicle speeds on those roads between 6 to 7 although there was a general upward trend in speeds on most road types. Various sampling issues encountered in the collection and analysis of the 7 data are discussed. KEYWORDS Vehicle speed, Speed limit, Driver behaviour, Urban road, Rural road, Statistics. The University of Adelaide 9 The views expressed in this report are those of the authors and do not necessarily represent those of the University of Adelaide or the funding organisations.

3 Summary A systematic and ongoing method of measuring vehicle speeds has been introduced in South Australia to assess the effects of speed reduction countermeasures and to monitor the speed behaviour of South Australian motorists over time. This report documents the initial collection of speed data at sites in South Australia in 7. The sites selected included sites with historical measurements supplemented by new sites to give a broad range of road types. Speed data was collected for one week at each of the sites and summary volume and speed statistics and speed distributions are given for each of the road types surveyed. Limited historical surveys on a set of roads in built up areas indicated that travelling speeds on those roads fell in (after the introduction of the default km/h speed limit in March ) compared to and fell again in. However, travelling speeds on those roads increased in 7 compared to by a statistically significant amount at least on Adelaide local roads affected by the km/h limit. Analysis of previously collected data for a limited subset of rural roads indicated no statistically significant change in vehicle speeds on those roads between 6 to 7 although there was a general upward trend in speeds on most road types. Various sampling issues encountered in the collection and analysis of the 7 data are discussed with the aim of ensuring future valid and meaningful speed surveys. CASR Road Safety Research Report Vehicle speeds in South Australia 7 iii

4 Contents Introduction... Methodology.... Site selection.... Data collected... Traffic volumes and speeds in All vehicles.... Free speed vehicles... 9 Changes in speeds from to 7 on roads in built up areas.... All vehicles.... Free speed vehicles... Changes in speeds from 6 to 7 on rural roads.... All vehicles.... Free speed vehicles... 6 Discussion Baseline speed measurements Changes in speeds from to 7 on roads in built up areas Changes in speeds from 6 to 7 on rural roads Sampling issues Further analysis... 9 Acknowledgements... References... Appendix A - Site locations... iv CASR Road Safety Research Report Vehicle speeds in South Australia 7

5 Introduction Speed is an important determinant of crash incidence and outcome and numerous initiatives are being implemented in South Australia with the aim of reducing the speeds of vehicles. A systematic and ongoing method of measuring vehicle speeds in South Australia has been introduced to assess the effects of speed reduction countermeasures and to monitor the speed behaviour of motorists over time. The Department for Transport, Energy and Infrastructure contracted CASR to identify a selection of sites in South Australia at which speed measurements will be taken at on a yearly basis. The sites selected included sites with historical measurements supplemented by new sites to give a broad range of road types. The process of selection can be found in the following reports (Woolley, 8; Woolley and Kloeden, 8). This Report summarises the data collected at the selected sites in 7 which forms the baseline for future surveys. Some comparisons are also made with previous years for sites with previously collected survey data. CASR Road Safety Research Report Vehicle speeds in South Australia 7

6 Methodology. Site selection The full process of site selection can be found in Woolley (8) and Woolley and Kloeden (8). Note that some of the sites mentioned in those reports were dropped from the current study due to placement near a change in speed limit or misidentification of a speed limit zone. Table. lists the origin of the sites that formed the final set of survey sites. The individual site locations are listed in Appendix A. Table. Speed survey sites by road type and survey source Road type (speed limit) Auslink site Harwood site* Default site New measured site Adelaide local () 8 8 Adelaide collector () Adelaide arterial two way no median (6) 6 Adelaide arterial two way with median (6) 6 Adelaide arterial multi-lane no median (6) 6 Adelaide arterial multi-lane with median (6) 9 Adelaide arterial (8) 6 6 Rural local () Rural arterial (6) Rural hills arterial (8) Rural arterial () 6 Rural arterial () Outback arterial () Total * named after Colin Harwood who initiated data collection at these sites The Auslink sites are DTEI controlled permanent measurement sites that record the speed of all passing vehicles throughout the year with data downloads being performed manually at about weekly intervals. The data for August 7 was requested for each of the sites and a week of data at each site was selected for analysis. The last week of August was selected except where equipment malfunctions required an earlier week in August to be used. August was chosen as the month that best represents average traffic flows on these roads. The Harwood sites represent a selection of sites that DTEI has for some years been conducting speed measurements at for a one week period in August. Note that three of the listed Auslink sites are also Harwood sites and the Auslink data for 7 was used for analysis. The 6 speed data for all Harwood sites was also obtained for comparison purposes. The default sites were those used in the evaluation of the introduction of the default km/h speed limit. One of the original sites was dropped as it was found to be a collector road with a 6 km/h speed limit. These sites were surveyed by a contractor for one day each in, and in November or December and this data is used for comparison purposes. These sites were surveyed by a contractor again in 7 for a full week mostly in November or December. Some sites had to be remeasured in early 8 due to equipment malfunction. The new measured sites were additional sites surveyed by the same contractor collecting the default data during the same time period in November and December 7. They were selected to bolster the number of sites in the different road types, mainly Total CASR Road Safety Research Report Vehicle speeds in South Australia 7

7 concentrating on metropolitan arterial roads. The rural hills arterial sites consisted of six sites with 8 km/h speed limits where infrequent DTEI speed measurements were made in the past. However, two of these were dropped: one was actually a km/h speed zone; and one was very close to a km/h speed limit zone.. Data collected The data was collected in most cases using a standard traffic counter box and tubes that were set up by either a contactor or DTEI personnel. At some sites, in-ground detectors were used for measurements. The following information was recorded for each vehicle that passed during the survey period: date time (to nearest second) direction of travel speed (to nearest. km/h) wheelbase (to nearest. m) headway (to nearest. second) gap (to nearest. second) number of axles class of vehicle (based on number of axles and wheel bases) The aim was to capture data at each site for a continuous one week period either in August 7 or November 7 depending on the site. Due to equipment malfunctions, some of the time periods had to be extended but a full week of data was collected at each of the sites. Due to limitations of the equipment, multilane arterial roads with medians had their median lanes measured and multilane arterial roads without medians had their kerbside lanes measured. CASR Road Safety Research Report Vehicle speeds in South Australia 7

8 Traffic volumes and speeds in 7 This Section presents summary traffic volume and speed statistics for each road type for a full week of data collection at each of the sites listed in Appendix A.. All vehicles The traffic volume and summary speed statistics for all vehicles passing the measured sites over a one week period are presented in Table. grouped by road type. Road type (speed limit) Table. Traffic volumes and speed statistics for each road type in 7 Number of sites Vehicle count Mean speed Median speed 8th percentile speed %exceeding speed limit %exceeding speed limit by more than km/h Adelaide local () Adelaide collector () Adelaide arterial two way no median (6) Adelaide arterial two way with median (6) Adelaide arterial multi-lane no median (6) Adelaide arterial multi-lane with median (6) Adelaide arterial (8) Rural local () Rural arterial (6) Rural hills arterial (8) Rural arterial () Rural arterial () Outback arterial () CASR Road Safety Research Report Vehicle speeds in South Australia 7

9 Figures. -.8 present the speed distributions of the various road types. Figure. Speed distributions for km/h Adelaide local roads and Adelaide collector roads in Adelaide local () Adelaide collector () Figure. Speed distributions for km/h Adelaide local roads and rural local roads in 7 Adelaide local () Rural local () CASR Road Safety Research Report Vehicle speeds in South Australia 7

10 Figure. Speed distributions for 6 km/h Adelaide arterial two way roads by presence of a median in Adelaide arterial two way no median (6) Adelaide arterial two way with median (6) Figure. Speed distributions for 6 km/h Adelaide arterial two way roads by presence of a median in Adelaide arterial multi-lane no median (6) Adelaide arterial multi-lane with median (6) CASR Road Safety Research Report Vehicle speeds in South Australia 7

11 Figure. Speed distributions for 8 km/h Adelaide arterial roads and rural hills arterial roads in 7 6 Adelaide arterial (8) Rural hills arterial (8) Figure.6 Speed distributions for km/h rural local roads and 6 km/h rural arterial roads in Rural local () Rural arterial (6) CASR Road Safety Research Report Vehicle speeds in South Australia 7 7

12 Figure.7 Speed distributions for km/h rural arterial roads and km/h rural arterial roads in 7 Rural arterial () Rural arterial () Figure.8 Speed distributions for km/h rural arterial roads and outback arterial roads in 7 Rural arterial () Outback arterial () CASR Road Safety Research Report Vehicle speeds in South Australia 7

13 . Free speed vehicles Free speed vehicles were defined as those that had at least a four second headway gap to the vehicle in front of them (ie the time between the front wheels of the two vehicles passing the measurement site was at least four seconds). The drivers of free speed vehicles presumably all make a choice of what speed to travel at unlike the drivers of vehicles in a platoon that are limited to the speed of the front vehicle. By examining just free speed vehicles, freely chosen speeds can be analysed. Table. shows the percentage of vehicles on each road type that were travelling at a free speed as defined above. Not surprisingly the road types with greater traffic flows tended to have a lower proportion of free speed vehicles travelling on them (due to greater traffic congestion). Table. Percentage of vehicles travelling at a free speed for each road type in 7 Road type (speed limit) Total vehicles Free speed vehicles % free speed Adelaide local () Adelaide collector () Adelaide arterial two way no median (6) Adelaide arterial two way with median (6) Adelaide arterial multi-lane no median (6) Adelaide arterial multi-lane with median (6) Adelaide arterial (8) Rural local () Rural arterial (6) Rural hills arterial (8) Rural arterial () Rural arterial () Outback arterial () CASR Road Safety Research Report Vehicle speeds in South Australia 7 9

14 The traffic volume and summary speed statistics for free speed vehicles passing the measured sites over a one week period are presented in Table. grouped by road type. Road type (speed limit) Table. Free speed traffic volumes and speed statistics for each road type in 7 Number of sites Vehicle count Mean speed Median speed 8th percentile speed %exceeding speed limit %exceeding speed limit by more than km/h Adelaide local () Adelaide collector () Adelaide arterial two way no median (6) Adelaide arterial two way with median (6) Adelaide arterial multi-lane no median (6) Adelaide arterial multi-lane with median (6) Adelaide arterial (8) Rural local () Rural arterial (6) Rural hills arterial (8) Rural arterial () Rural arterial () Outback arterial () Figures present the free speed distributions of the various road types. Figure.9 Free speed distributions for km/h Adelaide local roads and Adelaide collector roads in Adelaide local () Adelaide collector () CASR Road Safety Research Report Vehicle speeds in South Australia 7

15 Figure. Free speed distributions for km/h Adelaide local roads and rural local roads in 7 Adelaide local () Rural local () Figure. Free speed distributions for 6 km/h Adelaide arterial two way roads by presence of a median in Adelaide arterial two way no median (6) Adelaide arterial two way with median (6) CASR Road Safety Research Report Vehicle speeds in South Australia 7

16 Figure. Free speed distributions for 6 km/h Adelaide arterial two way roads by presence of a median in Adelaide arterial multi-lane no median (6) Adelaide arterial multi-lane with median (6) Figure. Free speed distributions for 8 km/h Adelaide arterial roads and rural hills arterial roads in 7 6 Adelaide arterial (8) Rural hills arterial (8) CASR Road Safety Research Report Vehicle speeds in South Australia 7

17 Figure. Free speed distributions for km/h rural local roads and 6 km/h rural arterial roads in Rural local () Rural arterial (6) Figure. Free speed distributions for km/h rural arterial roads and km/h rural arterial roads in 7 Rural arterial () Rural arterial () CASR Road Safety Research Report Vehicle speeds in South Australia 7

18 Figure.6 Free speed distributions for km/h rural arterial roads and outback arterial roads in 7 Rural arterial () Outback arterial () CASR Road Safety Research Report Vehicle speeds in South Australia 7

19 Changes in speeds from to 7 on roads in built up areas In, just before the introduction of the default km/h speed limit in built up areas of South Australia, the speeds of vehicles were measured for one day at sites (a week day with a preference for Wednesdays where possible). These measurements were repeated approximately one year later in and again in in order to assess the effect of the introduction of the default km/h speed limit on vehicle speeds (Kloeden, Woolley, McLean;, 6). Since the current set of surveyed sites includes of these sites it is possible to compare speeds in 7 with those measured in, and. The individual sites are identified in Appendix A. Since the sites in earlier years were only surveyed for one day of the week, data for that day was taken from each of the relevant sites in 7.. All vehicles The combined traffic volume and speed statistics by year of survey for each type of road are presented in Tables. -.. Note that all the km/h roads were zoned at 6 km/h during the survey. Green numbers indicate a decrease in a speed measurement from the previous survey and red numbers indicate an increase in a speed measurement from the previous survey. Table. Traffic volumes and speed statistics for km/h rural local roads by year of survey ( sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h Table. Traffic volumes and speed statistics for km/h Adelaide local roads by year of survey (8 sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h CASR Road Safety Research Report Vehicle speeds in South Australia 7

20 Table. Traffic volumes and speed statistics for km/h Adelaide collector roads by year of survey ( sites) Measurement Year of survey 7 Traffic count 6 68 Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h Table. Traffic volumes and speed statistics for 6 km/h Adelaide arterial roads by year of survey ( sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding 6 km/h % exceeding 7 km/h.... The change in mean speed over the surveys for each road type is shown graphically in Figure.. Note that all the km/h roads were zoned at 6 km/h during the survey. Figure. Change in mean speeds over time by road type Mean speed (km/h) Year of survey Adelaide arterial roads (6) Adelaide collector roads () Rural local roads () Adelaide local roads () 6 CASR Road Safety Research Report Vehicle speeds in South Australia 7

21 The speed distributions in the 7 survey are compared with the speed distributions in the survey for each road type in Figures. -.. Figure. Speed distributions for km/h rural local roads by year of survey ( sites) Figure. Speed distributions for km/h Adelaide local roads by year of survey (8 sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7 7

22 Figure. Speed distributions for km/h Adelaide collector roads by year of survey ( sites) Figure. Speed distributions for 6 km/h Adelaide arterial roads by year of survey ( sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

23 It is clear that the measured speeds increased from to 7 on all of these four road types. However, a certain variation in daily speed measurements is to be expected so it is not clear if the change in speeds can be attributed to an underlying effect or to chance variation in the measurements. In order to test the statistical significance of the change in speed, each site/direction combination was treated as a single measurement with a before and after speed value and the changes in these values over the relevant sites were analysed. As an example, consider the mean speed on Adelaide local roads in 7 compared to. There were 8 such sites (one of which was a one way street) giving independent collections of speed measurements in each year. Taking the mean speed of each collection in and 7 gives pairs of mean speeds and changes in mean speed. If all of the changes were in the same direction, then it would be likely that any overall difference was not the result of chance. If, however, close to half were in one direction and half were in the other direction (by about the same amounts), then the individual changes would likely have been due to chance. In the particular case under examination, 7 changes showed an increase in mean speed and 8 showed a decrease in mean speed and the average change over all pairs was an increase of. km/h. The probability of achieving such a result if there were no underlying effect is calculated using a matched pair t-test as. (ie only one time in ). We can therefore conclude that it is highly likely that mean speeds on Adelaide local roads went up because of an underlying effect rather than through chance variation and that the average increase per site was. km/h. This method was extended to all road types and traffic volume and speed measures and the average changes are presented in Table. with the statistically significant results marked. Road type (speed limit) Table. Average changes at sites in 7 compared to by road type Number of speed collections Vehicle count Mean speed Median speed 8th percentile speed %exceeding speed limit %exceeding speed limit by more than km/h Rural local () Adelaide local () -.7.*.*.6..6 Adelaide collector () Adelaide arterial (6) 7.6* All roads 8.9.7*.7*..86*.9 All of the above roads 7.68*.66*.66*.*.9*. * statistically significant (p <.) CASR Road Safety Research Report Vehicle speeds in South Australia 7 9

24 . Free speed vehicles The combined traffic volume and speed statistics by year of survey for each type of road are presented for free speed vehicles in Tables Free speed vehicles were defined as those that had at least a four second headway gap to the vehicle in front of them (ie the time between the front wheels of the two vehicles passing the measurement site was at least four seconds). Note that all the km/h roads were zoned at 6 km/h during the survey. Green numbers indicate a decrease in a speed measurement from the previous survey and red numbers indicate an increase in a speed measurement from the previous survey. Table.6 Free speed traffic volumes and speed statistics for km/h rural local roads by year of survey ( sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h Table.7 Free speed traffic volumes and speed statistics for km/h Adelaide local roads by year of survey (8 sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h Table.8 Free speed traffic volumes and speed statistics for km/h Adelaide collector roads by year of survey ( sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h CASR Road Safety Research Report Vehicle speeds in South Australia 7

25 Table.9 Free speed traffic volumes and speed statistics for 6 km/h Adelaide arterial roads by year of survey ( sites) Measurement Year of survey 7 Traffic count Mean speed Median speed th percentile speed % exceeding 6 km/h % exceeding 7 km/h The change in mean free speed over the surveys for each road type is shown graphically in Figure.6. Note that all the km/h roads were zoned at 6 km/h during the survey. Figure.6 Change in mean free speeds over time by road type Mean speed (km/h) Year of survey Adelaide arterial roads (6) Adelaide collector roads () Rural local roads () Adelaide local roads () CASR Road Safety Research Report Vehicle speeds in South Australia 7

26 The free speed distributions in the 7 survey are compared with the free speed distributions in the survey for each road type in Figures Figure.7 Free speed distributions for km/h rural local roads by year of survey ( sites) Figure.8 Free speed distributions for km/h Adelaide local roads by year of survey (8 sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

27 Figure.9 Free speed distributions for km/h Adelaide collector roads by year of survey ( sites) Figure. Free speed distributions for 6 km/h Adelaide arterial roads by year of survey ( sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

28 The method explained at the end of Section. was applied to all road types to determine the average changes in traffic volume and speed measures along with the statistical significance of those results for free speed vehicles (see Table.). Table. Average changes at sites in 7 compared to by road type for free speed vehicles Road type (speed limit) Number of speed collections Vehicle count Mean speed Median speed 8th percentile speed %exceeding speed limit %exceeding speed limit by more than km/h Rural local () Adelaide local () -9.*.*.7*... Adelaide collector () Adelaide arterial (6) -6.* All roads *.7*..7*. All of the above roads -9.87*.7*.7*.*.*.7 * statistically significant (p <.) CASR Road Safety Research Report Vehicle speeds in South Australia 7

29 Changes in speeds from 6 to 7 on rural roads The Harwood sites represent a selection of rural sites that DTEI has for some years been conducting speed measurements at for a one week period in August (named after the initiator of the surveys, Colin Harwood). The 6 speed data for all Harwood sites was obtained for comparison with the 7 speed data. The individual sites are identified in Appendix A.. All vehicles The combined traffic volume and speed statistics by year of survey for each type of road are presented in Tables. -.. Green numbers indicate a decrease in a speed measurement from the previous survey and red numbers indicate an increase in a speed measurement from the previous survey. Table. Traffic volumes and speed statistics for rural local roads by year of survey ( km/h speed limit - sites) Measurement Year of survey 6 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h.8.7 Table. Traffic volumes and speed statistics for rural arterial roads by year of survey (6 km/h speed limit - sites) Measurement Year of survey 6 7 Traffic count Mean speed Median speed th percentile speed % exceeding 6 km/h % exceeding 7 km/h..77 Table. Traffic volumes and speed statistics for rural arterial roads by year of survey ( km/h speed limit - 6 sites) Measurement Year of survey 6 7 Traffic count 99 9 Mean speed Median speed th percentile speed.7.8 % exceeding km/h % exceeding km/h CASR Road Safety Research Report Vehicle speeds in South Australia 7

30 Table. Traffic volumes and speed statistics for rural arterial roads by year of survey ( km/h speed limit - 6 sites) Measurement Year of survey 6 7 Traffic count 7 Mean speed.. Median speed.9. 8th percentile speed.. % exceeding km/h..7 % exceeding km/h..86 Table. Traffic volumes and speed statistics for outback arterial roads by year of survey ( km/h speed limit - sites) Measurement Year of survey 6 7 Traffic count Mean speed..97 Median speed th percentile speed 9.. % exceeding km/h.86. % exceeding km/h..9 The changes in mean speeds between 6 and 7 for each road type are shown graphically in Figures. and.. 6 Figure. Change in mean speeds over time by rural road type (low speed limit roads) 9 Rural arterial roads (6) Rural local roads () Mean speed (km/h) Year of survey 6 CASR Road Safety Research Report Vehicle speeds in South Australia 7

31 Figure. Change in mean speeds over time by rural road type (high speed limit roads) Mean speed (km/h) Outback arterial roads () 97 Rural arterial roads () 96 Rural arterial roads () Year of survey The speed distributions in the 7 survey are compared with the speed distributions in the 6 survey for each road type in Figures Figure. Speed distributions for rural local roads by year of survey ( km/h speed limit - sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7 7

32 Figure. Speed distributions for rural arterial roads by year of survey (6 km/h speed limit - sites) Figure. Speed distributions for rural arterial roads by year of survey ( km/h speed limit - 6 sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

33 Figure.6 Speed distributions for rural arterial roads by year of survey ( km/h speed limit - 6 sites) Figure.7 Speed distributions for outback arterial roads by year of survey ( km/h speed limit - sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7 9

34 The method explained at the end of Section. was applied to all road types to determine the average changes in traffic volume and speed measures along with the statistically significance of those results (see Table.6). Road type (speed limit) Table.6 Average changes at sites in 7 compared to 6 by rural road type Number of speed collections Vehicle count Mean speed Median speed 8th percentile speed %exceeding speed limit %exceeding speed limit by more than km/h Rural local () Rural arterial (6) Rural arterial ().67* Rural arterial () Outback arterial () 6 9.* All roads <= 6 km/h 6.8* All roads > 6 km/h.* All of the above roads.9* * statistically significant (p <.) CASR Road Safety Research Report Vehicle speeds in South Australia 7

35 . Free speed vehicles The combined traffic volume and speed statistics by year of survey for each type of road are presented for free speed vehicles in Tables As previously free speed vehicles were defined as those that had at least a four second headway gap to the vehicle in front of them (ie the time between the front wheels of the two vehicles passing the measurement site was at least four seconds). Table.7 Traffic volumes and speed statistics for rural local roads by year of survey ( km/h speed limit - sites) Measurement Year of survey 6 7 Traffic count Mean speed Median speed th percentile speed % exceeding km/h % exceeding 6 km/h.8.9 Table.8 Traffic volumes and speed statistics for rural arterial roads by year of survey (6 km/h speed limit - sites) Measurement Year of survey 6 7 Traffic count 66 6 Mean speed Median speed th percentile speed % exceeding 6 km/h % exceeding 7 km/h.8. Table.9 Traffic volumes and speed statistics for rural arterial roads by year of survey ( km/h speed limit - 6 sites) Measurement Year of survey 6 7 Traffic count Mean speed Median speed th percentile speed.6.8 % exceeding km/h % exceeding km/h CASR Road Safety Research Report Vehicle speeds in South Australia 7

36 Table. Traffic volumes and speed statistics for rural arterial roads by year of survey ( km/h speed limit - 6 sites) Measurement Year of survey 6 7 Traffic count Mean speed.6.8 Median speed.6.6 8th percentile speed.9.6 % exceeding km/h.6. % exceeding km/h.. Table. Traffic volumes and speed statistics for outback arterial roads by year of survey ( km/h speed limit - sites) Measurement Year of survey 6 7 Traffic count Mean speed.6 6. Median speed th percentile speed % exceeding km/h.. % exceeding km/h..8 The changes in mean free speeds between 6 and 7 for each road type are shown graphically in Figures. and.. Figure.8 Change in mean free speeds over time by rural road type (low speed limit roads) 6 9 Rural arterial roads (6) Rural local roads () Mean speed (km/h) Year of survey CASR Road Safety Research Report Vehicle speeds in South Australia 7

37 Figure.9 Change in mean free speeds over time by rural road type (high speed limit roads) Mean speed (km/h) Outback arterial roads () 97 Rural arterial roads () 96 Rural arterial roads () Year of survey The free speed distributions in the 7 survey are compared with the free speed distributions in the 6 survey for each road type in Figures Figure. Free speed distributions for rural local roads by year of survey ( km/h speed limit - sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

38 Figure. Free speed distributions for rural arterial roads by year of survey (6 km/h speed limit - sites) Figure. Free speed distributions for rural arterial roads by year of survey ( km/h speed limit - 6 sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

39 Figure. Free speed distributions for rural arterial roads by year of survey ( km/h speed limit - 6 sites) Figure. Free speed distributions for outback arterial roads by year of survey ( km/h speed limit - sites) CASR Road Safety Research Report Vehicle speeds in South Australia 7

40 The method explained at the end of Section. was applied to all road types to determine the average changes in traffic volume and speed measures along with the statistical significance of those results for free speed vehicles (see Table.). Road type (speed limit) Table. Average changes at sites in 7 compared to 6 by rural road type Number of speed collections Vehicle count Mean speed Median speed 8th percentile speed %exceeding speed limit %exceeding speed limit by more than km/h Rural local () Rural arterial (6) Rural arterial ().7* Rural arterial () Outback arterial () 6.* All roads <= 6 km/h 79.8* All roads > 6 km/h 7.7* All of the above roads.98* * statistically significant (p <.) 6 CASR Road Safety Research Report Vehicle speeds in South Australia 7

41 6 Discussion 6. Baseline speed measurements Speed measurements at sites around South Australia have been collected and will form the baseline against which future surveys at the same set of sites will be compared. There were equipment malfunctions at some sites, necessitating the recollection of data at those sites early in 8. For future surveys, the speed collection contractor should forward collected data as soon as possible for verification so that problem sites can be resampled closer to the target time period. Rural local roads and outback arterial roads had the greatest proportion of vehicles exceeding the posted speed limit by more than km/h (more than % of vehicles in each case). 6. Changes in speeds from to 7 on roads in built up areas A subset of the 7 survey sites on Adelaide roads had single day speed surveys conducted in, and as part of the evaluation of the introduction of the default km/h urban speed limit. This allowed changes in speeds from to 7 to be examined. Previous reports on this data found reductions in speeds on all the road types examined from to and further reductions from to (Kloeden, Woolley and McLean;, 6). When examining a comparable subset of the 7 speed data, speeds on all the examined road types increased from to 7. Further analysis found that the increase was only statistically significant for Adelaide local roads. However, the relative consistency of the increase on different road types and the fact that the increase achieves statistical significance when all road types were combined suggest that the increase in travelling speeds observed is unlikely to be due to chance. The best estimate of the size of the change for all the examined roads is a.66 km/h increase in mean vehicle speeds and.7 km/h for mean free vehicle speeds from to Changes in speeds from 6 to 7 on rural roads A subset of the 7 survey sites on rural roads had comparable speed surveys conducted in 6 (as part of the Harwood series of surveys). This allowed changes in speeds from 6 to 7 to be examined on those roads. Although there were indications of a slight increase in speeds on these roads from 6 to 7, further analysis found no statistically significant difference in any of the speed measures between the two years. 6. Sampling issues There are a number of sampling issues that need to be taken into consideration when carrying these speed surveys forward. Random variation When taking repeated samples of traffic flows at a specific location, a certain variation in mean speed is to be expected even if driver speeding behaviour remains unchanged due simply to the random nature of traffic. This means that a change in mean speed at a given site from one year to the next cannot be considered as meaningful in a general context. The solution to this problem is to sample multiple sites and conduct statistical tests on the consistency of any changes across the sites. The more sites used, the smaller the overall CASR Road Safety Research Report Vehicle speeds in South Australia 7 7

42 change can be and still be considered as being unlikely to be due to chance alone. This is the reason for the large number of sites in the survey. It also has implications for looking at subsets of the surveyed sites: when small subsets are examined, only very large changes can be considered to be unlikely to be due to chance. Time of year It is reasonable to assume that the speed distribution of vehicles changes throughout the year. Given that data is being collected for one week at each site, it is important to avoid school holidays, public holidays and other special events that could conceivably affect traffic speeds. Both August and November (the target survey months) contain no school or public holidays. Ideally, surveys should be conducted at a specific site during the same week every year and it is important to make every effort to achieve this goal. A detailed discussion of the advantages of permanent monitoring sites was made in Woolley (8) and Woolley and Kloeden (8). At the time of these surveys there were no permanent monitoring sites in the metropolitan area compared to approximately in rural areas. Weather conditions Large fluctuations in rainfall and temperature from one year to the next could be expected to affect vehicle volumes and speeds. It may be worth monitoring rainfall and temperature during the survey periods with a view to changing the sampling window when large year to year variations are observed although this would mean collecting additional data at sites without continuous monitoring. This may also introduce additional time of year differences so it is not an ideal solution. Road works Road works can have a large affect on vehicle speeds. For this reason site measurements are delayed if road works are in progress at a given site. An attempt should be made to avoid scheduling road works at the survey sites during the survey times. Traffic incidents Short term disruptions to traffic (ie road crashes, short term road work, broken down vehicles, nearby events with large crowds) can affect the resultant speed distributions. The collection of data for a full week will minimise the effect of these disruptions on the overall speed distribution but the effect could still be a significant one. It may be worthwhile comparing vehicle counts and speeds during the week for each site between surveys and eliminating or controlling for obvious large changes in traffic patterns or speeds. Changes to roads It is possible that the physical layout of a survey site may change or that surrounding changes to roads and lighting sequences may affect the traffic patterns at the survey site. This needs to be monitored both by physically checking the sites each year and examining the traffic flow and speed distributions for unexpected changes. Enforcement practices Enforcement practices can affect the speeds of vehicles on a given section of road. If sites identified as having a high proportion of speeding vehicles in this study are targeted by police because of this, then the sites in this study will no longer be representative of roads in general. It is for this reason that details of the actual location of sites is not presented in 8 CASR Road Safety Research Report Vehicle speeds in South Australia 7

43 this report. An alternate approach would be to obtain the cooperation of the police in avoiding enforcement at or near the survey locations during the survey periods. Calibration of equipment The amphometer tubes used to collect data should be placed one metre apart. If this distance is out by one centimetre the error in speed at 6 km/h will be.6 km/h which is around the size of the effects that are to be expected. It is therefore important that the equipment is checked and calibrated after it is installed. 6. Further analysis This report examines the overall speed and free speed distributions of traffic at the surveyed locations. However, the datasets collected contain much more data than this. Examination of the hour of day and day of week traffic volume and speed data would be valuable. Vehicles are also identified in the data by class and so travelling speeds by vehicle type could be explored along with a more detailed analysis of vehicle gaps. The effects of seasonal variation can also be explored at sites where continuous speed data has been collected. CASR Road Safety Research Report Vehicle speeds in South Australia 7 9

44 Acknowledgements This study was funded by the South Australian Department for Transport, Energy and Infrastructure (DTEI) through a Project Grant to the Centre for Automotive Safety Research. The DTEI Project Manager was Tamra Fedojuk. The Centre for Automotive Safety Research receives core funding from both the South Australian Department for Transport, Energy and Infrastructure and the South Australian Motor Accident Commission. The views expressed in this report are those of the authors and do not necessarily represent those of the University of Adelaide or the funding organisations. CASR Road Safety Research Report Vehicle speeds in South Australia 7

45 References Kloeden CN, Woolley JE, McLean AJ () Evaluation of the km/h default urban speed limit in South Australia. Adelaide: Centre for Automotive Safety Research. Kloeden CN, Woolley JE, McLean AJ (6) Further evaluation of the South Australian default km/h speed limit. Adelaide: Centre for Automotive Safety Research. Woolley JE (8) Regular speed surveys on South Australian roads. Adelaide: Centre for Automotive Safety Research. Woolley JE, Kloeden CN (8) A methodology for regular speed surveys on South Australian roads. Adelaide: Centre for Automotive Safety Research. CASR Road Safety Research Report Vehicle speeds in South Australia 7

46 Appendix A - Site locations Tables A. - A. give the locations of the sites measured in the 7 survey grouped by the road type. The locations with survey years, and were also surveyed for a one day period in those years as part of the evaluation of the introduction of the default km/h urban speed limit. The locations with a survey year of 6 had a one week period surveyed in that year as part of the Harwood series of survey (note that annual surveys were conducted at the Hardwood sites back to but that data is not analysed here). Table A. Adelaide local roads ( km/h speed limit) Road ID Suburb Survey years LM Rosewater,,, 7 LM Beverley,,, 7 LM Maylands,,, 7 LM Campbelltown,,, 7 LM Seacliff Park,,, 7 LM6 Kilburn,,, 7 LM7 Smithfield Plains,,, 7 LM8 Salisbury East,,, 7 LM9 Glenelg North,,, 7 LM Broadview,,, 7 LM Marleston,,, 7 LM Paralowie,,, 7 LM Salisbury East,,, 7 LM Glenelg South,,, 7 LM Beverley,,, 7 LM6 Adelaide,,, 7 LM7 North Adelaide,,, 7 LM8 Payneham South,,, 7 Table A. Adelaide collector roads ( km/h speed limit) Road ID Suburb Survey years CM Netherby,,, 7 CM West Beach,,, 7 CM Noarlunga Downs,,, 7 CM Stirling,,, 7 CM Largs Bay,,, 7 CM6 Hallett Cove,,, 7 CM7 Hackham,,, 7 CM8 Kidman Park,,, 7 CM9 Norwood,,, 7 CM St Peters,,, 7 CM Novar Gardens,,, 7 CASR Road Safety Research Report Vehicle speeds in South Australia 7

47 Table A. Adelaide arterial two way roads with no median (6 km/h speed limit) Road ID Suburb Survey years AA Happy Valley,,, 7 AA Clapham,,, 7 AA Kent Town,,, 7 AA Findon 7 AA Pennington 7 AA6 Flinders Park 7 Table A. Adelaide arterial two way roads with a median (6 km/h speed limit) Road ID Suburb Survey years AB Blair Athol,,, 7 AB Newton 7 AB St Peters 7 AB Tranmere 7 AB Keswick 7 AB6 Ethelton 7 Table A. Adelaide arterial multi-lane roads with no median (6 km/h speed limit) Road ID Suburb Survey years AC Cumberland Park,,, 7 AC Burnside,,, 7 AC Warradale 7 AC Fullarton 7 AC Evandale 7 AC6 Ridleyton 7 Table A.6 Adelaide arterial multi-lane roads with a median (6 km/h speed limit) Road ID Suburb Survey years AD Fullham Gardens,,, 7 AD Newton,,, 7 AD Manningham,,, 7 AD Brooklyn Park,,, 7 AD Salisbury Downs 7 AD6 Hectorville 7 AD7 Clarence Gardens 7 AD8 Warradale 7 AD9 Para Hills 7 Table A.7 Adelaide arterial roads (8 km/h speed limit) Road ID Suburb Survey years AM Salisbury Park 7 AM West Beach 7 AM Morphett Vale 7 AM Gilles Plains 7 AM Modbury North 7 AM6 O'Halloran Hill 7 CASR Road Safety Research Report Vehicle speeds in South Australia 7

48 Table A.8 Rural local roads ( km/h speed limit) Road ID Suburb Survey years LR Mount Gambier,,, 7 LR Mount Gambier,,, 7 LR Millicent,,, 7 LR Naracoorte,,, 7 LR Berri,,, 7 LR6 Berri,,, 7 LR7 Renmark,,, 7 LR8 Barmera,,, 7 LR9 Port Augusta,,, 7 LR Port Augusta,,, 7 LR Crystal Brook,,, 7 LR Wallaroo,,, 7 LR Freeling 6, 7 LR Nuriootpa 6, 7 Table A.9 Rural arterial roads (6 km/h speed limit) Road ID Suburb Survey years CR Clare 6, 7 CR Port Lincoln 6, 7 CR Naracoorte 6, 7 CR Waikerie 6, 7 Table A. Rural hills arterial roads (8 km/h speed limit) Road ID AH 7 AH 7 AH 7 AH 7 Survey years Table A. Rural arterial roads ( km/h speed limit) Road ID Survey years AR 6, 7 AR 6, 7 AR 6, 7 AR 6, 7 AR 6, 7 AR6 6, 7 AR7 7 AR8 7 AR9 7 AR 7 CASR Road Safety Research Report Vehicle speeds in South Australia 7

49 Table A. Rural arterial roads ( km/h speed limit) Road ID Survey years HR 6, 7 HR 6, 7 HR 6, 7 HR 6, 7 HR 6, 7 HR6 6, 7 HR7 7 HR8 7 HR9 7 HR 7 HR 7 HR 7 HR 7 HR 7 HR 7 HR6 7 HR7 7 HR8 7 HR9 7 HR 7 HR 7 HR 7 HR 7 HR 7 HR 7 HR6 7 HR7 7 HR8 7 HR9 7 HR 7 HR 7 HR 7 HR 7 HR 7 HR 7 Table A. Outback arterial roads ( km/h speed limit) Road ID Survey years BR 6, 7 BR 6, 7 BR 6, 7 CASR Road Safety Research Report Vehicle speeds in South Australia 7